The present invention relates generally to an ink jet head, an ink jet apparatus and a method of recoverably activating in the apparatus.
In the case that the ink jet apparatus is kept unused for a long time or in the case that some specific ejecting ports among a plurality of ejecting ports is rarely used compared with other ejecting ports, there sometimes arises a malfunction that ink is improperly ejected from the ejecting ports. The reason why the foregoing improper ink ejection occurs consists in that water in ink is evaporated from the ejection ports or water in ink is evaporated from an ink chamber communicated with the ejection ports. In addition, there arises another malfunction that some ink droplets, some water droplets or dust particles adhere to the ejection surface of an ink jet head having a plurality of ejecting ports formed thereon, causing each ejected ink droplets to be pulled by the adhered foreign materials with the result that the ejecting direction is deviated from a predetermined one.
To prevent the foregoing malfunction from arising, a conventional ink jet apparatus is equipped with means as noted below to serve as a so-called ejection recovering system. This ejection recovering system is exemplified by e.g., preliminary ejecting means for discharging ink having an increased viscosity in a predetermined ink receiving medium prior to each recording operation, ink sucking means for removing some adhered materials from ejecting ports and a common ink chamber by sucking ink therefrom, ink sucking means for removing air bubbles introduced in ink at the time of ink reservoir replacement, and capping means for preventing water in ink from being vaporized from ejecting ports.
However, the conventional ejection recovering system has some following problems. Specifically, the ink jet apparatus is unavoidably fabricated at an increased cost attributable to necessity for disposing the preliminary ejecting means, the ink sucking means or the capping means. In addition, it is practically difficult to design and construct the ink jet apparatus with small dimensions because of necessity for reserving a space required for disposing the preliminary ejecting means, the ink absorbing means or the capping means. Additionally, it is necessary that an ink reservoir, a suction pump and associated pipings are arranged for executing preliminary ejection or ink suction, and moreover, accumulatively store waste ink in a certain container.
With respect to an ink jet apparatus capable of recording colored images, development works have been hitherto conducted for providing an ink jet apparatus including an ink jet head having plural groups of ejecting ports for black ink, yellow ink, magenta ink and cyan ink formed thereon, ink reservoirs independently disposed corresponding the groups of ejecting ports, a recovering cap common to the ejecting ports, and an ejection recovering unit. This kind of ink jet apparatus is often designed and constructed to record an image colored with two or three kinds of colors other than black. In this case, when a quantity of color ink per one dot is equalized to that of black ink, the diameter of a printed dot recorded on a recording medium is excessively enlarged. In view of the foregoing fact, when each dot is recorded with color ink, the diameter of each injecting port is reduced or the cross-sectional area of an injection nozzle is reducibly varied. To practice a so-called bubble jet recording system for ejecting liquid droplets by heating electrothermal transducers, a measure is taken such that a surface area of each heating elements is reduced or a distance between the heat generating element and an ejection orifice is changed to another one.
An ink jet apparatus using plural kinds of inks each having a different color and/or different depth of color employed therefor includes an ink jet head or an ink jet head unit having plural groups of ejecting ports formed therein, and the nozzle cross-sectional area of each ejecting port among a group of ejecting ports and the diameter of the same each varies from plural groups of ejecting ports. In addition, this ink jet apparatus includes an ejection recovering unit but this ejection recovering unit has the following shortages. Specifically, in the case that a magnitude of resistance against flowing of ink differs from each of plural groups of ejection ports and a sucking operation is achieved by a common recovering cap, a quantity of ink sucked by a single recovering operation each varies from plural groups 23 of ejecting ports. Consequently, a large quantity of ink is sucked by each ejection port among a group of ejecting ports having a large flow rate coefficient but a small quantity of ink is sucked by each ejection port among a group of ejecting ports having a small flow rate coefficient. If a quantity of ink sucked by each ejecting port during each sucking operation each varies from plural groups of ejecting ports, ink should be sucked from plural groups of ejecting ports in such a manner as to match with the quantity of ink sucked by the group of ejecting ports where a magnitude of resistance against flowing of ink is maximized, in order to remove air bubbles introduced in ink at the time of ink reservoir replacement or discharge ink having an increased viscosity in an ink path. For this reason, a quantity of ink in excess of a required quantity is sucked from other groups of ejecting ports and then uselessly wasted therefrom.
A flow rate coefficient of plural groups of ejection ports adapted to eject plural kinds of inks each having a different kind of color and/or different depth of color is substantially determined depending on a sum of the cross-sectional area of each ejecting ports involved in each of plural groups of ejecting ports. Obviously, the sum of the cross-sectional area of all the ejecting ports is determined based on the cross-sectional area of each ejecting port and the number of ejecting ports. Thus, in the case that plural groups of ejecting ports each having a different flow rate coefficient are subjected to ejection recovering treatment by utilizing the pressure in the fully capped state in consideration of the current technical tendency for reducing the number of components constituting the ink jet apparatus and simplifying the structure of the ink jet apparatus, the aforementioned malfunctions are liable to arise.
The present invention has been made in consideration of the aforementioned background.
An object of the present invention is to provide an ink jet head for an ink jet apparatus which assures that a quantity of uselessly consumed ink when the ink jet head is recoverably activated can be reduced.
Another object of the present invention is to provide an ink jet apparatus in which an ink jet head of the foregoing type is installed.
Further object of the present invention is to provide a method of recoverably activating an ink jet apparatus of the foregoing type.
According to a first aspect of the present invention, there is provided an ink jet head including plural groups of ejecting ports each having a different flow rate coefficient, wherein a capacity of an ink path communicated with a group of ejecting ports having a small flow rate coefficient is smaller than that of an ink path communicated with a group of ejecting ports having a large flow rate coefficient.
In addition, according to a second aspect of the present invention, there is provided an ink jet apparatus having an ink jet head of the foregoing type installed therein, wherein the ink jet head includes plural groups of ejecting ports each having a different flow rate coefficient in such a manner that a capacity of an ink path communicated with a group of ejecting ports having a small flow rate coefficient is smaller than that of an ink path communicated with a group of ejecting ports having a large flow rate coefficient, and sucking means is arranged for sucking ink from the plural group of ejecting ports in the state that the latter are fully covered with a common recovering cap.
Additionally, according to a third aspect of the present invention, there is provided a method of recoverably activating an ink jet apparatus including plural groups of ejecting ports each having a different flow rate coefficient by utilizing the pressure applied to the ejecting ports, all the plural groups of ejecting ports being subjected to ejection recovering treatment, wherein the method comprises a step of discharging the ink remaining in the region extending from the plural groups of ejecting ports to predetermined positions in a plurality of ink paths communicated with the plural groups of ejecting ports and a step of allowing ink discharging positions to be dislocated to the predetermined positions in the plurality of ink paths to positionally coincide with the same in the substantially same timing relationship after the ejection recovering treatment starts to be conducted. In other words, a characterizing feature of this method consists in that limitative positions where ink is discharged from an ink path including a common ink chamber communicated with ejecting ports involved in a certain group of ejection ports on the common basis and an ink feeding path from which ink is fed to the common ink chamber are substantially positionally coincident with each other among plural groups of ejection ports.
With this construction, e.g., the ink remaining in the ink path extending from the ejecting ports to a joint portion between the ink feeding path and the ink chamber is discharged in the substantially same timing relationship after the ejection recovering treatment starts to be conducted. Otherwise, e.g., the ink remaining in the region extending from the ejecting ports to the joint portion between the ink path and an ink reservoir is discharged in the substantially same timing relationship.
In this case, according to the present invention, since the ink reservoir usually has a comparatively large capacity, the aforementioned technical problem does not substantially arise with the ink reservoir. Therefore, it is not necessary that the foregoing part of the ink reservoir is involved in the ink path of the present invention.
The ink reservoir serving to feed ink to the ink reservoir can be integrated with the ink jet head. Otherwise, the ink reservoir can be arranged so as to be separated from the ink jet head. It is acceptable that partitioning means for partitioning a group of ejecting ports having a different flow rate coefficient from each other is disposed in the recovering cap.
According to the present invention, since a sum of the capacity of the ink feeding path and the capacity of the common chamber is determined depending on the flow rate coefficient of each nozzle, ejection recovering treatment can reliably be conducted for each of the group of ejection ports by performing an ejection recovering operation with the aid of a single recovering cap, whereby a quantity of ink to be uselessly wasted during each ejection recovering operation can be reduced. In other words, a small quantity of ink to be sucked during each ejection recovering operation is discharged from a group of ejecting ports having a small nozzle flow rate coefficient, and moreover, a quantity of ink required for removing air bubbles in ink having an increased viscosity can be reduced. Thus, it is possible to recoverably activate the ink jet head without fail.
The above and other objects, effects, features and advantages of the present invention will become apparent from the following description which of embodiments thereof taken in conjunction with the accompanying drawings.